Gap Between Neanderthals and Us Narrows, But Does Not Close

Were the Neanderthals evolutionary also-rans—or just like modern humans?

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Some researchers have come to the conclusion that there were no strong behavioral differences between Neanderthals (reconstruction above) and modern humans.

PHOTOGRAPH BY JOE MCNALLY, NATIONAL GEOGRAPHIC

Neanderthals have traditionally been viewed as human evolution's also-rans. Yes, they had brains as big as ours, made fairly complex stone tools, and flourished across a huge expanse of Eurasia for nearly 300,000 years. But they vanished, while our ancestors not only survived but also took over the planet.

This discrepancy has led scientists for decades to try to pinpoint what specific inadequacy led to the Neanderthal's demise—or, put the other way around, what special property it is that makes us fully human and them not quite ... enough. Was it complex language that they lacked? Hunting prowess? The capacity to innovate?

In a recent paper in the journal PLOS One, Paola Villa of the University of Colorado Museum in Boulder and Wil Roebroeks of Leiden University in the Netherlands review the archaeological evidence for these and other often-touted Neanderthal inferiorities. In every case, they find no evidence to support the contention that Neanderthals were any different than the modern human beings living in Africa and the Middle East at the same time. In Villa and Roebroeks' view, the Neanderthals never really went extinct at all. They are us—or at least they live on in the genomes of modern humans living outside Africa today. (See "Why Am I Neanderthal?")

Twenty years ago or so, the story of modern human origins seemed pretty simple: Homo sapiens arose in Africa and replaced everybody everywhere else including the Neanderthals, who went extinct. Can you briefly say what's changed to complicate that picture now?

My version is that we had our origins in Africa maybe 150,000-200,000 years ago; we came out of Africa about 60,000 years ago and replaced all the other groups living outside of Africa. Twenty years ago I would have said the interbreeding between us and them was insignificant. That was certainly wrong. We know now that there was interbreeding going on, at least on a small scale, not only between us and the Neanderthals, but also between us and the Denisovans, another form of archaic human known from DNA from a cave in Siberia. (Read "The Case of the Missing Ancestor" in National Geographic magazine.)

Paolo Villa and Wil Roebroeks argue that the Neanderthals weren't so much replaced as absorbed into the larger modern human population. Would you agree?

We know that the Neanderthals disappeared soon after modern humans came into western Europe over 40,000 years ago. We don't know exactly when the Denisovans disappeared, but after 40,000 years ago, only modern human fossils are known from eastern Asia. There was also a population of a very small human-like species on the island of Flores in Indonesia—often called "hobbits." It had been thought they were around until about 17,000 years ago, but unpublished evidence suggests they could have disappeared earlier, in which case the spread of modern humans might correlate with their demise.

I think I see where this is leading...

The common factor in all three disappearances is the arrival of modern humans. Villa and Roebroeks have been as fair as possible to the Neanderthals, and they've come to the conclusion that there were no strong behavioral differences between them and modern humans. But that isn't necessarily the whole story.

What parts are missing?

Well, even small differences in behavior could have been significant under the stressful conditions that prevailed much of the time for Neanderthals. For instance, we know that modern people had eyed sewing needles in Europe 35,000 years ago. If you have something like that, you can make tailored clothing, or a tent covered with sewn hides, and you get better insulation. You can keep your babies warm more reliably, which is absolutely critical for the survival of the next generation. I'm sure the Neanderthals had some kind of clothing—it would have been essential in Ice Age Europe. But having a sewing needle could make a big difference.

What about art?

Neither the Neanderthals nor the moderns in Africa had representational art before 60,000 years ago, so if we take that as the basis of comparison, there's no difference. But look at the statuettes from [the early Upper Paleolithic] in Germany beginning 40,000 years ago. You've got humans, animals, mythological creatures that combine human and animal parts.

So this would argue for a symbolic way of thinking that would express some behavioral advantage?

It suggests a really complex way of thinking. Neanderthals were certainly intelligent, and technologically they were very well equipped. They could make resins for mounting points on handles, they buried their dead—they have that level of complexity. But representational art suggests for some people a whole spiritual and religious dimension.

Then there's music. There is one flute that some researchers say is associated with Neanderthals from a site in Slovenia, but it's very disputed; a number of people who studied it think it's a natural object with some holes in it made by bear teeth. But when you get to the sites in Germany, there are undoubted, complete flutes made from the wing bones of vultures and from mammoth ivory, several of them 35,000-40,000 years old.

But when comparing Neanderthals to the modern humans around at the same time as they were, Villa and Roebroeks don't see any difference in symbolic behavior.

To be fair, yes, we don't find flutes in Africa 60,000 years ago—and representational art, you can't find that either. I can see where they're coming from. And I agree with them that there is no one thing that led to our success and the Neanderthal's demise. In my earlier books, I took the view that there was a major behavioral gap between the Neanderthals and us. Recent evidence has considerably narrowed that gap—but I don't think it has completely closed.

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So why did they go extinct, if they were very much like us?

Neanderthals disappeared at different times in different parts of Eurasia. The reasons why they disappeared from Britain could differ from the reasons why they disappeared in Gibraltar or the Middle East. People were looking for a single cause. It's got to be more complicated.

You mentioned that conditions were very stressful for Neanderthals through much of their time. What role did climate play in their disappearance?

We know that the climate was extremely unstable from about 70,000 years ago to about 12,000 years ago. Every few thousand years, the climate switched, often very rapidly. In northern Europe and Asia, at times it could change in less than ten years from being almost as warm as the present day, to being so cold there would be icebergs floating in the Mediterranean Sea. Imagine in the lifetime of a Neanderthal in Europe, or a Denisovan over in Siberia, suddenly everything you're familiar with, all the animals and plants—they're all gone. Lots of those populations of humans are going to die out; they can't adapt to such rapidly changing conditions.

Wouldn't that apply to modern humans as well?

Modern humans suffered too. They also seem to disappear if it's extremely cold. But their overall population history is quite different.

The genetic evidence suggests that half a million years ago, the Neanderthals, Denisovans, and modern humans had the same effective population size: They were all a single population, which I think of as belonging to the species Homo heidelbergensis. Through time, it split into three distinct populations: In western Europe and Asia it became the Neanderthals, in east Asia the Denisovans, and in Africa it became us, Homo sapiens.

The genetic data suggests that the Neanderthal and Denisovan population numbers sank steadily until they go extinct some 50,000 years ago. There was never a long-enough period of stability for them to build their numbers up to a large size. Whereas in Africa, the modern humans' numbers are maintained, even for a while increasing. If temperatures drop 5-10 degrees in Africa, you're not going to die; there may be changes in rainfall and desert and forest and so forth, but that temperature drop probably won't kill you.

In Britain, or Siberia, these populations were constantly under pressure. When it was really cold, they were surviving in pockets in the south—in the Iberian Peninsula, the Italian peninsula, the Balkans, maybe in India and Southeast Asia. All the area to the north would empty of people. Then when it warms up, people would start to expand north and grow their numbers. But often they only had 3,000 years before the temperature dropped all the way back again. So I think it is the climate that was shutting down the diversity of those populations; they couldn't maintain large numbers because of the climate wearing them down.

So it wasn't that the Neanderthals and Denisovans were cognitively disadvantaged. They just had a harder row to hoe.

Keeping your numbers low is bad news for cultural diversity as well. Think about modern populations today: There are so many of us, we are so well networked and have so many ways of storing information, that when something innovative appears, it takes root and gets built upon. But go back 50,000 or 100,000 years and it simply wasn't like that. You have small groups of people at times isolated from each other. That was certainly true of the Neanderthals. They lived in small groups and were not well networked. Under those circumstances, when your population crashes, you can lose cultural information. (See "Neanderthals Lived in Small, Isolated Populations, Gene Analysis Shows.")

How so?

Imagine a tribe of 30 Neanderthals, and there are two or three people who are specialists in making fire. Imagine a disease hits, or there's an accident, and those three firemakers die. Now no one in the group knows how to make fire. So until the group can reconnect to another Neanderthal group, they've lost that knowledge. We see this in the modern hunter-gatherer groups who at times lose the knowledge of making fire at will, or the knowledge of making boats. As Villa and Roebroeks are arguing, it's not necessarily that the Neanderthals were stupid. They had the dice weighted against them.

What do you think happened when Neanderthals and modern humans met?

My model is that modern humans came out of Africa 60,000 years ago and moved very quickly into the territory of the Neanderthals, later into the territory of the Denisovans, and soon after that into the territory of the "hobbits." Within 20,000 years, as far as we can tell, those other populations have gone, all of them. Modern humans moving into those areas would be hitting the same environment, gathering the same plants, wanting to live in the best sites. There would have been economic competition.

But the genetic evidence clearly shows that these groups were interbreeding with each other. Doesn't that suggest they weren't outcompeted as much as assimilated?

Obviously there was some interbreeding, or we wouldn't have that ancient DNA showing up in people outside Africa today. But the amount is quite low, [at] about 2 percent of Neanderthal DNA and about 4 to 5 percent Denisovan DNA in people living today in Australia, New Guinea, and nearby. But that amount could have come from just a few interbreeding events. It doesn't have to be widespread interbreeding over the whole range; you can argue that there's no evidence of any interbreeding in western Europe at all.

What do you think accounts for our unending fascination with Neanderthals?

It's this whole question of having a population of humans that are in some ways like us, and yet so different—and the fact that they died out and we're still here. And of course the fascination of the last five years is that they didn't go 100 percent extinct, because we've all got a little bit of them inside us.

You've been immersed in the study of Neanderthals your entire career. If you were able to go back and meet one, what would you most like to ask him?

I'd ask him to tell me a story, and I'd see how complex that story was. Because obviously, one of the unknowns is how similar their minds were to ours. Villa and Roebroeks aren't alone in saying there's no evidence that their minds were any different from ours. But I'm not sure. I'm sure they had speech and language, but I'm guessing it was much more a language for the here and now, a more practical language for survival. I doubt they would have expressed complicated things like, "Well, what if I did this differently, what then would happen?" The kind of hypothetical reasoning that leads to modern inventions. Maybe Neanderthals didn't have so much of that.

I might also ask the Neanderthal if he had ever seen those funny people with those high foreheads and dark skin—our modern human ancestors—and if he had, what did he think? Would he fancy one as a partner?